A lubricating oil composition for use for reduction gears of various industrial machines is required to have wear resistance for preventing wear of gears, etc.
As a method for improving wear resistance of a lubricating oil, in general, there are known a method of adding a phosphorus-sulfur-containing compound and a sulfur-containing compound to a lubricating oil (for example, see PTL 1), a method of adding a dialkyl trisulfide, a dithiophosphate, an acid phosphate and an alkylamine salt thereof, and further optionally an alkenylsuccinimide derivative, a molybdenum dithiophosphate, a molybdenum disulfide and the like in combination, for improving oxidation stability at high temperatures while securing wear resistance (for example, see PTL 2), etc.